Frank M. Wilhelm

Seasonal Food Habits of Bull Trout from a Small Alpine Lake in the Canadian Rocky Mountains

Abstract We investigated the seasonal diet of a native, undisturbed population of bull trout Salvelinus confluentus in an alpine lake to examine predation patterns between fish size-classes and in relation to available invertebrate prey. The diets of small (≤250 mm in fork length, FL) and large (>250 mm FL) bull trout were similar. Bull trout fed on seasonally abundant prey species. After ice-out in July, the diet was dominated by chironomid pupae. Daphnia pulex var. and the amphipod Gammarus lacustris dominated the diet in August and September. Both Daphnia and Gammarus reproduced before bull trout switched to preying on them in early August. Bull trout fed size-selectively on large individuals of both Daphnia and Gammarus. Large bull trout preyed on larger Daphnia than did small bull trout. Fish of both size-classes consumed large Gammarus. Bull trout were spatially segregated; small fish occupied shallow water (<1 m deep), while large fish occupied the profundal offshore zone. Spatial segregation preve...

Concentrations of organochlorine pesticides and polychlorinated biphenyls in amphipods (Gammarus lacustris) along an elevation gradient in mountain lakes of western Canada

Populations of the amphipod Gammarus lacustris were examined for their concentrations of organochlorine pesticides and polychlorinated biphenyls (PCBs) from seven lakes spanning a 1,300-m elevation gradient in Alberta, Canada. The concentrations of several of the semivolatile organochlorine compounds ([SVOCs], vapor pressure > 0.03 Pa at 20 degrees C) increased at higher altitudes. This pattern was generally not observed among the less volatile organochlorines ([LVOCs]. vapor pressure < 0.03 Pa at 20 degrees C). These same SVOC compounds have been previously shown to increase at high latitudes as a result of their long-range transport and preferential deposition in cold climates. We also show that populations of G. lacustris at high elevations have slower growth rates and store more lipids than populations at lower elevations. To resolve the colinearity of independent variables, we used multiple regression to identify patterns of contaminant concentrations in this data set. Multiple regressions showed that the effect of elevation, lipid content, and temperature on contaminant concentrations was no longer significant once the growth rate of Gammarus was included as an independent variable. This study shows that enrichment of SVOCs occurs in Gammarus at high altitudes in Alberta, Canada, and that growth rate (biodilution) appears to be the primary influence. Because Gammarus is an important trophic link in aquatic foodwebs in these environments, enhanced concentrations of toxicants in prey may increase their biomagnification in top predators of high-altitude lakes.

Experimental manipulation of TN:TP ratios suppress cyanobacterial biovolume and microcystin concentration in large-scale in situ mesocosms

Abstract A global dataset was compiled to examine relations between the total nitrogen to total phosphorus ratio (TN:TP) and microcystin concentration in lakes and reservoirs. Microcystin concentration decreased as TN:TP ratios increased, suggesting that manipulation of the TN:TP ratio may reduce microcystin concentrations. This relationship was experimentally tested by adding ammonium nitrate to increase the TN:TP ratio in large-scale (70 m3), in situ mesocosms located in a eutrophic reservoir that routinely experiences toxic blooms of cyanobacteria. At a TN:TP ratio >75:1, chlorophytes dominated the phytoplankton community in the mesocosms, while cyanobacterial biovolume was significantly reduced and microcystin was not detected. In contrast, the unmanipulated reservoir was dominated by cyanobacteria, and microcystin was detected. Secchi depths were 1.1 to 1.8 times greater in the mesocosms relative to the reservoir. Cladoceran zooplankton had a larger body size (0.14 mm on average) in the mesocosms compared to conspecifics in the reservoir, which was likely related to the higher quality food. Combined, these empirical and experimental data indicate that although nutrient addition is counterintuitive to current cyanobacteria management practices, increasing the TN:TP ratio by adding nitrogen may be a potential short-term management strategy to reduce cyanobacteria and cyanotoxins when other alternatives (e.g., phosphorus reduction) are not possible. Additional experimental studies with careful controls are needed to define best management practices and identify any potential unintended consequences before nitrogen addition is implemented as a lake and reservoir management practice.

SEASONAL TRENDS IN THE HEAD CAPSULE LENGTH AND BODY LENGTH/WEIGHT RELATIONSHIPS OF TWO AMPHIPOD SPECIES

[Amphipod body lengths and weights are important variables in life history, biomass and production determinations. Length and weight are often estimated from head capsule length-body length or weight relationships based on a single field collection. Possible seasonal variation in these relationships is rarely considered. We used seasonal data for two amphipod species (Gammarus lacustris and Diporeia hoyi) to test the hypothesis that head capsule length-body length/weight relationships remain seasonally constant. Slopes of monthly relationships were significantly different (ANCOVA). However, the differences in slope and intercept were trivial, and all monthly regressions yielded similar predictive results. Regressions based on pooled seasonal samples underestimated measured biomass by 5%, while predicted lengths varied between 0 to ± 2 mm from measured lengths. We conclude that head capsule length-body length/weight relationships for these amphipods are seasonally robust, and may be estimated from single collections provided all size classes are obtained. If all size classes can not be obtained from one sample, relationships should be based on pooled samples., Amphipod body lengths and weights are important variables in life history, biomass and production determinations. Length and weight are often estimated from head capsule length-body length or weight relationships based on a single field collection. Possible seasonal variation in these relationships is rarely considered. We used seasonal data for two amphipod species (Gammarus lacustris and Diporeia hoyi) to test the hypothesis that head capsule length-body length/weight relationships remain seasonally constant. Slopes of monthly relationships were significantly different (ANCOVA). However, the differences in slope and intercept were trivial, and all monthly regressions yielded similar predictive results. Regressions based on pooled seasonal samples underestimated measured biomass by 5%, while predicted lengths varied between 0 to ± 2 mm from measured lengths. We conclude that head capsule length-body length/weight relationships for these amphipods are seasonally robust, and may be estimated from single collections provided all size classes are obtained. If all size classes can not be obtained from one sample, relationships should be based on pooled samples.]

Population genetic study of the U.S. federally listed Illinois cave amphipod, Gammarus acherondytes

Worldwide, conservation personnel must balance the needs of endangered species and humans. Studies that provide information of a species’ genetic structure can identify conservation units and help prioritize populations. We used a region of the cytochrome c oxidase subunit I gene to examine the population genetics of the U.S. federally listed Illinois cave amphipod, Gammarus acherondytes. Eleven unique haplotypes were identified from nine populations in two hydrologically separate subregions, each of which contained genetically distinct populations. This conclusion is based on (i) subregions form clades in the interspecific phylogeographic analyses; (ii) the between-subregions component in the Analysis of Molecular Variance accounted for a significant fraction (81.45%) of the genetic variation; and (iii) no haplotypes were shared between subregions. These results coincide with the known distribution of G. acherondytes and regional hydrology. We recommend future recovery efforts avoid mixing individuals between subregions to prevent the breakdown of local adaptive gene complexes.

A Review of Managed Nitrate Addition to Enhance Surface Water Quality

Abstract Nitrate is a significant water pollutant with potential environmental impacts ranging from eutrophication to health risks to infants. But under certain circumstances nitrate may enhance water quality through a number of mechanisms, including enhancing oxidant capacity, regulation of redox potential, and suppression of nitrogen-fixing cyanobacteria. In this review the authors explore a range of case studies in which nitrate addition enhanced surface water quality including: purposeful addition of nitrate salts to lakes to repress internal phosphorus (P) loading, enhance organic matter oxidation, or impede bottom-water accumulation of methylmercury; purposeful and incidental addition of nitrate from point and nonpoint discharges to reservoirs and lakes; nitrogen (N) addition to lakes to affect phytoplankton and zooplankton composition; and nitrate addition to estuary sediment to repress hydrogen sulfide production. Nitrate addition decreased internal P and methylmercury loading, repressed sulfide production, and enhanced surface water quality by lowering total P, chlorophyll content, and phytoplankton dominance by cyanobacteria. No case study reported a worsening of eutrophic conditions due to nitrate addition, and a number of studies reported near complete loss of nitrate from the systems to which it was added. When purposely adding nitrate to anoxic surface waters, protocols should be used to maximize nitrate loss via biological denitrification but minimize enhancement of phytoplankton productivity. These protocols should include adding nitrate close to the sediment-water interface to promote nitrate loss via denitrification, managing the timing and magnitude of nitrate addition so that nitrate is depleted prior lake overturn in the fall, and not adding nitrate to N-limited systems. Elimination of existing N discharges to receiving waters should be implemented on a case-by-case basis with the awareness that nitrate in discharges may enhance surface water quality, particularly by suppressing internal P loading and associated phytoplankton productivity. In addition, managers and regulators should look to couple existing nitrate discharges with hypoxic water bodies in an effort to sustainably enhance water quality while removing nitrate from aquatic ecosystems via biological denitrification.

Bull trout population responses to reductions in angler effort and retention limits

Abstract We compared historical (1977–1980) and recent (1997–2001) abundance, catch-per-unit-effort (CPUE), and growth data to assess whether the implementation of restrictive sportfishing regulatory regimes in the 1990s led to changes in abundance and population structure of bull trout Salvelinus confluentus in two small Rocky Mountain lakes in Alberta, Canada. For remote Harrison Lake, we used changes in gill-net CPUE to infer a fivefold increase in bull trout abundance after closure of an access road and implementation of catch-and-release (CR) regulations. Bull trout growth rates decreased as their abundance increased. All large (fork length > 420 mm), old (age >12) bull trout were eliminated after regulatory changes were imposed. Reductions in prey abundance and size as bull trout abundance increased probably contributed to the demise of the large bull trout. For road-accessible Osprey Lake, no change in bull trout mark–recapture abundance estimates or growth rates were observed despite implementatio...

Estimating Reproductive Effort in Small Aquatic Invertebrates from Lipid Dynamics

ABSTRACT Invertebrates that brood eggs or offer parental care to developing embryos incur a cost of reproduction in addition to that associated with the production of eggs. This additional cost is difficult to quantify but it is important in shaping the reproductive strategy of organisms and for evaluating their life history trade-offs. I used lipid analyses to determine the energy expended by female amphipods during the incubation of eggs. Lipid levels in female Gammarus lacustris during incubation of eggs dropped from 18.2% after egg deposition into the brood pouch to 8.4% when young were released. This decrease equalled 13.0 J and was similar to the 14.6 J in lipid energy in the eggs.

Experimental additions of aluminum sulfate and ammonium nitrate to in situ mesocosms to reduce cyanobacterial biovolume and microcystin concentration

Abstract Recent studies suggest that nitrogen additions to increase the total nitrogen:total phosphorus (TN:TP) ratio may reduce cyanobacterial biovolume and microcystin concentration in reservoirs. In systems where TP is >100 μg/L, however, nitrogen additions to increase the TN:TP ratio could cause ammonia, nitrate, or nitrite toxicity to terrestrial and aquatic organisms. Reducing phosphorus via aluminum sulfate (alum) may be needed prior to nitrogen additions aimed at increasing the TN:TP ratio. We experimentally tested this sequential management approach in large in situ mesocosms (70.7 m3) to examine effects on cyanobacteria and microcystin concentration. Because alum removes nutrients and most seston from the water column, alum treatment reduced both TN and TP, leaving post-treatment TN:TP ratios similar to pre-treatment ratios. Cyanobacterial biovolume was reduced after alum addition, but the percent composition (i.e., relative) cyanobacterial abundance remained unchanged. A single ammonium nitrate (nitrogen) addition increased the TN:TP ratio 7-fold. After the TN:TP ratio was >50 (by weight), cyanobacterial biovolume and abundance were reduced, and chrysophyte and cryptophyte biovolume and abundance increased compared to the alum treatment. Microcystin was not detectable until the TN:TP ratio was <50. Although both treatments reduced cyanobacteria, only the nitrogen treatment seemed to stimulate energy flow from primary producers to zooplankton, which suggests that combining alum and nitrogen treatments may be a viable in-lake management strategy to reduce cyanobacteria and possibly microcystin concentrations in high-phosphorus systems. Additional studies are needed to define best management practices before combined alum and nitrogen additions are implemented as a reservoir management strategy.

Pollution of Aquatic Ecosystems I

The expanding human population and continuing pollution of aquatic resources threaten the survival of life on earth by reducing the quality and quantity of available water. Pollution sources are highly varied but can be categorized as point- and nonpoint source. Point source pollution is highly localized, easily identified, and relatively easily remedied. Nonpoint-source pollution, however, comes from diffuse sources and requires much greater effort to address. Loss of water, oxygen demands, and nutrient effects are examined in detail. Large impacts have been, and are, expected with continued water abstraction. Solutions include litigation and at worst armed conflict. Although oxygen demands from the addition of organic material can be significantly reduced by treating effluents, many parts of the world, especially developing countries, do not have the necessary funds or infrastructure. Significant progress has been made to relieve oxygen demand with in situ methods. These are expensive and require ongoing monitoring and maintenance. Excessive nutrients contribute to eutrophication, loss of oxygen, and ecosystem diversity. The recovery of some significant ecosystems after nutrient reductions is one of the not-so-dim parts of the chapter. Simply preventing aquatic pollution would be the most effective and least costly strategy to deal with it.